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    SubjectRe: [dm-devel] [RFC] training mpath to discern between SCSI errors
    Hannes Reinecke wrote:
    > Sergei Shtylyov wrote:
    >> Hello.
    >>
    >> Hannes Reinecke wrote:
    >>
    >>> Actually, I think we have two separate issues here:
    >>> 1) The need of having more detailed I/O errors even in the fs layer. This
    >>> we've already discussed at the LSF, consensus here is to allow other
    >>> errors than just 'EIO'.
    >>> Instead of Mike's approach I would rather use existing error codes
    >>> here;
    >>> this will make the transition somewhat easier.
    >>> Initially I would propose to return 'ENOLINK' for a transport failure,
    >>> 'EIO' for a non-retryable failure on the target, and 'ENODEV' for a
    >>> retryable failure on the target.
    >> Are you sure it's not vice versa: EIO for retryable and ENODEV for
    >> non-retryable failures. ENODEV looks more like permanent condition to me.
    >>
    > Ok, can do.
    > And looking a the error numbers again, maybe we should be using 'EREMOTEIO'
    > for non-retryable failures.
    >
    > So we would be ending with:
    >
    > ENOLINK: transport failure
    > EIO: retryable remote failure
    > EREMOTEIO: non-retryable remote failure
    >
    And here is the corresponding patch.
    Compile tested only; just to give an idea of the possible implementation.

    I have decided to pass the I/O failure information in-line:
    - scsi_check_sense() might now return 'TARGET_ERROR' to signal
    a permanent error
    - scsi_decide_disposition() sets the driver byte of the result
    field to 'DID_TARGET_FAILURE' if a return code of 'TARGET_ERROR'
    is encountered.
    - scsi_io_completion() sets the error to ENOLINK for DID_TRANSPORT_FAILFAST,
    EREMOTEIO for DID_TARGET_FAILURE, and EIO for any other error. It also
    resets DID_TARGET_FAILURE back to DID_OK once the error code is set.

    I'm not 100% happy with this patch; DID_TARGET_FAILURE is really just
    a communication vehicle to signal the permanent target failure.
    I looked at passing this information directly via an explicit argument
    to scsi_finish_command(), but this would include changing
    scsi_io_completion(), too. As both of them are exported / public
    interfaces I didn't like modifying them.

    Another possibility would be to re-use / redefine the 'DRIVER_'
    bits; they don't seem to be used a the moment. Eg 'DRIVER_HARD'
    for permanent errors, DRIVER_SOFT for link failures.

    Opinions welcome.

    Cheers,

    Hannes
    --
    Dr. Hannes Reinecke zSeries & Storage
    hare@suse.de +49 911 74053 688
    SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
    GF: Markus Rex, HRB 16746 (AG Nürnberg)
    From f0835d92426cb3938f79f1b7a1e1208de63ca7bc Mon Sep 17 00:00:00 2001
    From: Hannes Reinecke <hare@suse.de>
    Date: Mon, 30 Aug 2010 16:21:10 +0200
    Subject: [RFC][PATCH] scsi: Detailed I/O errors

    Instead of just passing 'EIO' for any I/O errors we should be
    notifying the upper layers with some more details about the cause
    of this error.
    This patch updates the possible I/O errors to:

    - ENOLINK: Link failure between host and target
    - EIO: Retryable I/O error
    - EREMOTEIO: Non-retryable I/O error

    'Retryable' in this context means that an I/O error _might_ be
    restricted to the I_T_L nexus (vulgo: path), so retrying on another
    nexus / path might succeed.

    Signed-off-by: Hannes Reinecke <hare@suse.de>

    diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
    index 487ecda..d49b375 100644
    --- a/drivers/md/dm-mpath.c
    +++ b/drivers/md/dm-mpath.c
    @@ -1270,7 +1270,7 @@ static int do_end_io(struct multipath *m, struct request *clone,
    if (!error && !clone->errors)
    return 0; /* I/O complete */

    - if (error == -EOPNOTSUPP)
    + if (error == -EOPNOTSUPP || error == -EREMOTEIO)
    return error;

    if (clone->cmd_flags & REQ_DISCARD)
    diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
    index ce089df..5da040b 100644
    --- a/drivers/scsi/scsi_error.c
    +++ b/drivers/scsi/scsi_error.c
    @@ -223,7 +223,7 @@ static inline void scsi_eh_prt_fail_stats(struct Scsi_Host *shost,
    * @scmd: Cmd to have sense checked.
    *
    * Return value:
    - * SUCCESS or FAILED or NEEDS_RETRY
    + * SUCCESS or FAILED or NEEDS_RETRY or TARGET_ERROR
    *
    * Notes:
    * When a deferred error is detected the current command has
    @@ -338,25 +338,25 @@ static int scsi_check_sense(struct scsi_cmnd *scmd)
    case COPY_ABORTED:
    case VOLUME_OVERFLOW:
    case MISCOMPARE:
    - return SUCCESS;
    + case DATA_PROTECT:
    + case BLANK_CHECK:
    + return TARGET_ERROR;

    case MEDIUM_ERROR:
    if (sshdr.asc == 0x11 || /* UNRECOVERED READ ERR */
    sshdr.asc == 0x13 || /* AMNF DATA FIELD */
    sshdr.asc == 0x14) { /* RECORD NOT FOUND */
    - return SUCCESS;
    + return TARGET_ERROR;
    }
    return NEEDS_RETRY;

    case HARDWARE_ERROR:
    if (scmd->device->retry_hwerror)
    return ADD_TO_MLQUEUE;
    - else
    - return SUCCESS;
    -
    + else {
    + return TARGET_ERROR;
    + }
    case ILLEGAL_REQUEST:
    - case BLANK_CHECK:
    - case DATA_PROTECT:
    default:
    return SUCCESS;
    }
    @@ -819,6 +819,7 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,
    case SUCCESS:
    case NEEDS_RETRY:
    case FAILED:
    + case TARGET_ERROR:
    break;
    case ADD_TO_MLQUEUE:
    rtn = NEEDS_RETRY;
    @@ -1512,6 +1513,12 @@ int scsi_decide_disposition(struct scsi_cmnd *scmd)
    rtn = scsi_check_sense(scmd);
    if (rtn == NEEDS_RETRY)
    goto maybe_retry;
    + if (rtn == TARGET_ERROR) {
    + /* Need to modify host byte to signal a
    + * permanent target failure */
    + scmd->result |= (DID_TARGET_FAILURE << 16);
    + rtn = SUCCESS;
    + }
    /* if rtn == FAILED, we have no sense information;
    * returning FAILED will wake the error handler thread
    * to collect the sense and redo the decide
    @@ -1529,6 +1536,7 @@ int scsi_decide_disposition(struct scsi_cmnd *scmd)
    case RESERVATION_CONFLICT:
    SCSI_LOG_ERROR_RECOVERY(3, sdev_printk(KERN_INFO, scmd->device,
    "reservation conflict\n"));
    + scmd->result |= (DID_TARGET_FAILURE << 16);
    return SUCCESS; /* causes immediate i/o error */
    default:
    return FAILED;
    diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
    index 9ade720..fb841e3 100644
    --- a/drivers/scsi/scsi_lib.c
    +++ b/drivers/scsi/scsi_lib.c
    @@ -736,8 +736,20 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
    memcpy(req->sense, cmd->sense_buffer, len);
    req->sense_len = len;
    }
    - if (!sense_deferred)
    - error = -EIO;
    + if (!sense_deferred) {
    + switch(host_byte(result)) {
    + case DID_TRANSPORT_FAILFAST:
    + error = -ENOLINK;
    + break;
    + case DID_TARGET_FAILURE:
    + cmd->result |= (DID_OK << 16);
    + error = -EREMOTEIO;
    + break;
    + default:
    + error = -EIO;
    + break;
    + }
    + }
    }

    req->resid_len = scsi_get_resid(cmd);
    @@ -796,7 +808,18 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
    if (scsi_end_request(cmd, error, good_bytes, result == 0) == NULL)
    return;

    - error = -EIO;
    + switch (host_byte(result)) {
    + case DID_TRANSPORT_FAILFAST:
    + error = -ENOLINK;
    + break;
    + case DID_TARGET_FAILURE:
    + cmd->result |= (DID_OK << 16);
    + error = -EREMOTEIO;
    + break;
    + default:
    + error = -EIO;
    + break;
    + }

    if (host_byte(result) == DID_RESET) {
    /* Third party bus reset or reset for error recovery
    @@ -1418,7 +1441,6 @@ static void scsi_softirq_done(struct request *rq)
    wait_for/HZ);
    disposition = SUCCESS;
    }
    -
    scsi_log_completion(cmd, disposition);

    switch (disposition) {
    diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
    index 8fcb6e0..abfee76 100644
    --- a/include/scsi/scsi.h
    +++ b/include/scsi/scsi.h
    @@ -397,6 +397,8 @@ static inline int scsi_is_wlun(unsigned int lun)
    * recover the link. Transport class will
    * retry or fail IO */
    #define DID_TRANSPORT_FAILFAST 0x0f /* Transport class fastfailed the io */
    +#define DID_TARGET_FAILURE 0x10 /* Permanent target failure, do not retry on
    + * other paths */
    #define DRIVER_OK 0x00 /* Driver status */

    /*
    @@ -426,6 +428,7 @@ static inline int scsi_is_wlun(unsigned int lun)
    #define TIMEOUT_ERROR 0x2007
    #define SCSI_RETURN_NOT_HANDLED 0x2008
    #define FAST_IO_FAIL 0x2009
    +#define TARGET_ERROR 0x200A

    /*
    * Midlevel queue return values.
    \
     
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      Last update: 2010-08-30 16:55    [W:0.033 / U:60.168 seconds]
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